Headers for combine harvesters are typically mounted on the feeder house of the combine to allow some floating action of the header relative to the feeder house so that the cutter bar can rest on the ground and float over the ground responsive to ground contours in a cutting action. To optimally follow ground contours, various attempts have been made to introduce some flexibility into the header.
U.S. Pat. No. 6,675,568 by Patterson et al discloses one example of a multi-section header with a flexible crop cutting knife for this purpose. The main frame structure of the header is formed in multiple sections including a centre section and two wing sections in which each section includes a skid element along the width thereof for riding along the ground. A balancing linkage is provided to distribute a total lifting force from the combine harvester into a central lifting force lifting the central section and first and section lifting forces for lifting the wing sections. Typically 90% of the lifting force is provided by the total lifting force from the combine harvester while the remaining lifting force is provided by the ground acting on the skid elements evenly across the width of the header. The header only operates in a flexible mode, however when cutting close to the ground so that the skids ride along the ground. When in a raised mode for cutting taller crops, the center and wing sections of the frame of the header are typically fixed relative to one another so that the entirety of the header is supported spaced above the ground by the lifting forces from the combine harvester. The suspension of the header on the combine harvester however still allows for some rolling movement about a forward extending axis, such that the outer ends of the wing sections can deviate substantially from the controlled height at the center of the header even when the header deviates only a few degrees from a parallel relationship to the ground due to the length of the header.
U.S. Pat. No. 8,245,489 by Talbot discloses a height control arrangement using gauge wheels supported at opposing ends of a rigid header. The gauge wheels serve to minimize any substantial deviations from a central controlled height of the header at the outboard ends of the header, however the system is only effective when used on a rigid header.